Hair drug testing differs from urine and saliva drug testing in the length of time from drug use to testing and in the impossibility of tampering with thedrug test to change the results. Cocaine, methamphetamines, opiates and phencyclidine are processed and undetectable after 72 hours in urine and 48 hours in saliva. They are, however, present in hair for up to 90 days after drug use.